1. Field of the Invention
The present invention relates to a Personal Identification System and, more particularly, to an improved arrangement in the verification position of such a system.
2. Description of the Prior Art
In U.S. patent application Ser. No. 229,085 filed on Jan. 28, 1982, an advanced Personal Identification System is described. The application entitled "Personal Identification System" was filed by the inventors Marvin Perlman and Milton Goldfine and assigned to the same assignee as the present application.
Briefly, the system described in said application comprises a generator which generates an Offset Number which is recorded on the magnetic stripe of a card, together with the account number (PAN) of the person to whom the card is to be issued. The generator stores transformed digits of a sequence of digits (IN) which have been secretly entered by one or more officers of the card-issuing institution. To generate the Offset Number the PAN is entered and transformed before initializing a first feedback shift register. The person to whom the card is to be issued enters a secretly chosen alphanumeric sequence (PIN), known only to him. The PIN, after undergoing a transformation initializes a second feedback shift register. When both registers have been initialized they are reinitialized by different parts of the representation of different digits of the transformed IN. The contents of a subset of the stages of the two registers are used to initialize a control feedback shift register which when reaching a selected state in its cycle of states assumes the timing and control of the generator during the derivation of the Offset Number, based on a selected mapping of the digits, then present, in the first and second feedback shift registers.
A credit card is entered into a verifier at the inception of a validation test of identity. Therein the PAN and Offset Number on the magnetic stripe on the card are read out. The user enters a secret PIN, and the verifier, like the generator, generates an Offset Number. Only if the PIN, entered into the verifier, is identical to that originally entered into the generator, does the verifier produce an Offset Number which is identical to that read off the card, thereby verifying the identity of the card user as the one to whom the card was issued.
The above described system, as disclosed in said application, represents a very significant break through in the state of the art in that it provides a higher degree of security than any attainable with any prior art system. However, as herebefore described, the verifier, to a very large degree, operates as the generator in that, like the generator, it generates an Offset Number. In addition, the verifier compares the Offset Number it generates with the one, present on the card's magnetic stripe, and only when the two are identical is an indication given that the person who entered the secret PIN has been identified as the rightful user of the card.
It is believed that an added degree of security may be achieved if the verifier were to operate in a mode different from that of the generator. This is partially based on the fact that whereas each generator will be located in a very secure location, where cards are to be issued, verifiers, however, will be present and transportable in the many thousands of establishments where cards can be used. Thus verifiers are accessible to unscrupulous people who may try to determine how the original generators produce valid PAN-PIN-OFFSET combinations. As described in said application, the verifier contains portions which make it practically impossible for one to open the verifier and completely analyze its mode of operation, and thereby determine the operation of the generator. It is believed, however, that an added degree of security may be attained by designing the verifier so that it does not mimic the behavior of the generator.